In the fabrication of integrated circuits it is necessary to prealign the silicon wafers prior to delivery to the work station. At the work station the wafer is then fine aligned prior to a circuit pattern being imprinted thereon. Prealignment is important inasmuch as the the wafer must be accurately enough positioned to be within the range of the fine alignment mechanism.
Presently available prealigners have the requirement that the wafer be centered, i.e., positioned in the X-Y direction before it can be angularly oriented. This is so inasmuch as the wafer can be delivered to the prealigner stage off-center by as much as half an inch which places it out of the range of any presently available angular orientation scheme.
The present invention overcomes the above problem and provides an accurate prealigner wherein the wafer may be angularly oriented without the necessity of first centering the wafer in the X-Y direction. In other words, the present invention is a prealigner which can angularly orient a wafer without the requirement of a integral X-Y centering stage.